1. Field of the Invention
The present invention relates to a remote center compliance (MRCC) device, which can correct automatically a location error or an angle error between parts incurred in an insertion work of machinery parts. More particularly, the present invention relates to a remote center compliance, which can be used in a force-insertion work that is a work for inserting a part and putting it together forcibly.
2. Background of the Related Art
As a device which easily correct a location error or an angle error between central axises of parts put together incurred in an insertion work that is a work for inserting a precise part such as a precise shaft, a pin and a bearing into a part having an inside diameter greater than an outside diameter of the precise part such as a shaft hole, a pin bole and a bearing bore and putting it together in order to smoothly perform the insertion work, U.S. Pat. Nos. 4,379,363 and 4,414,750 disclose a remote center compliance which automatically corrects, using a principle of elastic center, a location error or an angle error between parts.
Here, the principle of elastic center is referred to as a mechanical principle that when an elastic center is located near an object belonging to the remote center compliance device and an external force acting on the object passes through the elastic center, only a translation is performed in a direction of the external force without performing a rotation, and when a moment acts on the elastic center the object performs only a rotation centering on the elastic center without performing a translation.
Such a remote center compliance includes upper and lower structures coupled to each other by a plurality of elastic bodies symmetrically arranged centering on a central axis of the structures. The upper structure is held by an operating end of a robot or dedicated assembly apparatus, and the lower structure moving according to a principle of an elastic center includes a gripper holding a part inserted and put together.
As the elastic body an elastomer shear pad (ESP) including metal washers stacked in turn is often used. When the elastic bodies are appropriately arranged between the upper and lower structures, the elastic center exists on a central axis of the remote center compliance. The remote center compliance has a feature that an elastic repulsive force is relatively strong as to a direction of the central axis and is relatively weak as to a direction of behind and front and right and left and a twisting directing centering on the pivot.
When a precise shaft having a circular cross-section is inserted into a shaft hole to put together using an industrial robot or a dedicated assembly apparatus, a location error or angle error often occurs between the central axises of the parts inserted and put together. It is known that in order to smoothly perform the insertion work while correcting the location error or angle error, the elastic center is located near an end of the part to be inserted and put together.
FIG. 11 is a cross-sectional view illustrating a state that an insertion work is performed using a conventional remote center compliance device. The remote center compliance 1 is held by an operating end of a robot or dedicated assembly apparatus through a bracket 10, and a precise shaft 6a is inserted into a shaft hole 7a to put together. The remote center compliance 1 includes an upper structure 2 held by the bracket 10 and a lower structure 3 having a gripper 8 holding the precise shaft 6a. Even though a plan view of the remote center compliance 1 is omitted, three elastic bodies 4 are arranged with a phase 120xc2x0 on a concentric circle centering on a central axis C of the remote center compliance 1 and are inclined somewhat to the central axis C to couple the upper and lower structures 2 and 3.
The remote center compliance 1 is designed such that an elastic center P thereof is located around an end portion of the precise shaft 6a held by the gripper 8 according an arrangement of the respective elastic bodies 4. When a location error e occurs between the precise shaft 6a and the shaft hole 7a, when the precise shaft 6a is moved in a straight line of a direction V, an end portion of the precise shaft 6a contacts an angled portion f of the shaft hole 7a to cause a repulsive force R.
At this point, the contact force R is defined by a horizontal component force Rx and a vertical component force Rz. The horizontal component force Rx passes through the elastic center P and so performs only a translation in horizontal direction without causing a rotation. On the other hands, the vertical component force Rz acts as a moment centering on the elastic center P. But, since a repulsive force of the central axis C is very strong in the elastic center P of the remote center compliance 1, few rotations occurs in the lower structure 3.
Therefore, as shown in FIG. 12, the precise shaft 6a performs a translation along the angled portion f of the shaft hole 7a and then is inserted into the shaft hole 7a. In the insertion work of the precise part, an angle error incurred at an initial stage is a fatal ground of an inferior assembly, and thus it is very important to align the elastic center P with an end portion of the part to be inserted and put together.
As described above, when a precise part such as a precise shaft, a pin, and a bearing having a circular shaped cross section is inserted by an industrial robot or a dedicated assembly apparatus using the remote center compliance device, an excessive insertion force which may occur due to a location error and an angle error between assembly parts can be prevented in advance. As a result, since a bad influence on the robot or the assembly apparatus and part damages can be suppressed, product quality and work efficiency can be improved, and a high-precision assembly line can be co constructed at a low cost.
However, the conventional remote compliance performs a relatively loose insertion work smoothly by automatically correcting a location error or an angle error between the central axises of the parts to be inserted and put together. On the other hands, in a tight insertion work, i.e., force-insertion work in which an outside diameter of the part (e.g., precise shaft) to be inserted is greater than an inside diameter of the part (e.g., shaft hole), an insertion force of hundreds to thousands of kgf is required. Such a strong insertion force may destroy the elastic bodies. Therefore, the conventional remote center compliance cannot be used in a force-insertion work. In other words, even though the conventional remote center compliance corrects a location error between the central axises of the parts to be put together, when any of the elastic bodies becomes bent due to a strong insertion force, the part held by the lower structure is inclined so that the force-insertion work cannot be performed properly.
To overcome the problems described above, preferred embodiments of the present invention provide a remote center compliance device, which can be used in a force-insertion work as well as an insertion work.
In order to achieve the above object, the preferred embodiments of the present invention provide a remote center compliance device, comprising: upper and lower structures arranged in parallel to face each other; a plurality of elastic bodies coupling the upper and lower structures around a central axis of the remote center compliance; and three or more polar-type limiters of the same height installed on a first structure of one of the upper and lower structures around the central axis to extend toward a second structure of the other, wherein the limiters are arranged such that at least one limiter exists in each of both sides as to a straight line passing through the central axis on a plane vertical to the central axis, wherein each of the limiters includes a head portion having a wide section area on the end portion thereof and screw portions on the lower portion thereof, a gap t is given between a flat contact portion on an upper surface of the limiter and an upper surface of the upper structure, a gap u is given between an outer circumference of the head portion and an inside surface of a hole (2b) and the gap t is set to be smaller in shear transformation limit than an elastic displacement xcex4c of an axis direction and be identical to a predetermined elastic displacement xcex4s, so that when a predetermined elastic displacement of an up-and-down direction occurs in the elastic bodies, the predetermined elastic displacement of the elastic bodies is restricted by supporting a contact surface installed on an end portion of the respective limiters by a bedplate installed on the second structure, wherein the limiters are arranged such that at least one limiter exists in each of both sides as to a straight line passing through the central axis on a plane vertical to the central axis, so that when a predetermined elastic displacement of an up-and-down direction occurs in the elastic bodies, the predetermined elastic displacement of the elastic bodies is restricted by supporting a contact surface installed on an end portion of the respective limiters by a bedplate installed on the second structure.
A hole receiving the end portion of the limiter is installed in a portion of the second structure corresponding to a portion of the first structure where the limiter is installed, and the bedplate supporting the contact surface is installed in a member fixed to a opposite surface of the hole into which the end portion of the limiter is inserted.
The present invention further provides a remote center compliance, comprising: upper and lower structures arranged in parallel to face each other; a plurality of elastic bodies coupling the upper and lower structures around a central axis of the remote center compliance; and a limiting cover installed on a first structure of the other, wherein a gap t is given between a contact portion on an upper surface of the limiting cover and a bed plate, a gap u is given between an outer circumference of the lower structure and an inner circumference of a lower end portion in which a diameter of the limiting cover becomes large and the gap t is set to be smaller in shear transformation limit than an elastic displacement xcex4c of an axis direction and be identical to a predetermined elastic displacement xcex4s, so that when a predetermined elastic displacement of an up-and-down direction occurs in the elastic bodies, the predetermined elastic displacement of the elastic bodies is restricted by supporting a contact surface installed on an end portion of the limiting cover by a bedplate installed on an outer circumference portion of the second structure.
The upper structure is the first structure. The elastic body includes rubber plates and metal washers which are stacked in turn, and a predetermined elastic displacement is set to be smaller in shear transformation limit of the elastic body than an elastic displacement of an axis direction.